The present invention relates to a concave mirror, and more particularly relates to a concave mirror which magnifies an original picture projected on a screen or generated by a cathode-ray tube and which projects the magnified picture on another screen arranged at a long distance from the concave mirror, in a projector for a flight simulator and so forth.
In the projector for the flight simulator, a ship-maneuvering simulator and so forth, the screen or the cathode-ray tube for the original picture is generally set in the vicinity of a focus of the concave mirror so that the original picture on the screen or the cathode-ray tube is magnified on the other screen arranged at a long distance from the concave mirror. In this case, it is necessary for a size of the concave mirror to be large.
A kind of the large-size concave mirror is composed of a plurality of small-size concave glass mirrors joined together. Another kind of the large-size concave mirror is a thin mirror sheet whose periphery is fixed and whose mirror surface is deformed by a vacuum to form a concave mirror surface, the degree of which vacuum is controlled in accordance with a measured shape of the concave mirror surface to maintain a predetermined concave shape of the mirror surface. When the large-size concave mirror is composed of the plurality of small-size concave glass mirrors, it is necessary for each of the small-size concave glass mirrors to have a chamfer between the mirror surface and each of the joining surfaces of the glass mirrors and a weight of concave mirror is great. And when the small-size concave glass mirrors are not correctly fixed in a radial direction extending from a focus of the large-size concave mirror toward a mirror surface of the large-size concave mirror, the mirror surface is not made smooth by joining lines between the small-size concave glass mirrors. When the large-size concave mirror is the thin mirror sheet, the predetermined concave shape of the mirror surface can not be maintained, because the concave mirror surface is vibrated by a vibration of the simulator during operation thereof. Therefore, in the conventional projectors, the magnified and projected picture is disturbed by the joining lines between the small-size concave glass mirrors or by the vibrating concave mirror surface.